Cairo, Egypt (CNN) -- Pro-democracy activists in Cairo's Tahrir Square endured waves of attacks by people armed with machetes, knives, Molotov cocktails and horsewhips, according to opposition forces and witnesses.

Assaults began late Tuesday, leaving at least 44 people injured, opposition activists said, and they continued into Wednesday in the square, which was the center of the Egyptian protest movement that led to the removal of President Hosni Mubarak last month.

The activists said protesters -- who have a permanent encampment in the square -- were assaulted by gangs supporting the country's security apparatus, a remnant of the Mubarak regime.

Gunshots were heard in the square Wednesday afternoon.

Complaints about police corruption and abuses were among the top grievances of demonstrators who forced Mubarak from office.

Demonstrators also were angry about Mubarak's 30-year rule, a lack of free elections and economic issues, such as high food prices, low wages and high unemployment.

Since the president's departure, several thousand people have protested in Tahrir Square to urge Egypt's new rulers to implement promised reforms.

They have pressed Egypt's Supreme Council to end an emergency law and release political prisoners, among other things. They also have demanded civilian representation in government.

A British Foreign Office minister was to meet with Prime Minister Essam Sharaf, other top officials and opposition leaders in Egypt during a two-day visit that began Wednesday.

Before the visit, Alistair Burt said he urged officials "to work quickly towards free and fair democratic elections" and looks forward to spending time "with some of those who inspired such a profound change in the country's direction." He also said he plans to discuss the crisis in Libya and the Middle East peace process.

Wednesday's violence came on the same day that Nobel Peace laureate Mohamed ElBaradei announced that he will run for president in upcoming elections. The dissident reformist who served as director-general of the U.N.'s nuclear watchdog agency from 1997 to 2009 announced his decision on ONTV, a privately owned Egyptian television channel.

During his remarks, he called for the current constitution to be scrapped and replaced by a new one. He said his campaign would focus on education and health care for all, especially the poor.

In clashes unrelated to the political demonstrations, 13 people were killed Tuesday in skirmishes between Coptic Christians and Muslims in the capital, state-run television said. About 90 were wounded in the clashes, Egypt's health minister, Dr. Ashraf Hatem, said.